The use of support energy in the meat processing industry

Download The use of support energy in the meat processing industry

Post on 15-Jun-2016




2 download


J. Sci. Fd Agric. 1978,29, 172-181 The Use of Support Energy in the Meat Processing Industry J. Keith Jacques and Kenneth L. Blaxter* Department of Management Science and Technology Studies, University of Stirling, Stirling, Scotland, and *The Rowett Research Institute, Bucksburn, Aberdeen, Scotland (Manuscript received 22 August 1977) A study of the consumption of support energy in the meat industry in Scotland involved both large meat factories and high street butchers. The energy cost of transport of live animals from farms to abattoirs was 0.5 x lo9 J/ton deboned meat for both pigs and cattle. Factory slaughtering, butchery and processing costs were 60 x lo9 J/ton deboned meat for pigs and 41 x 109 J/ton for cattle. When on-farm costs are included the support energy subsidy/ton meat was similar for both species at 110 x lo9 J/ton deboned meat. The energy subsidy incurred in meat factories/ton deboned meat varied with the extent of processing, from 27 x lo9 J/ton forjointed pork to 86 x l o 9 J for beef pies containing 34% meat. The imparting of convenience to food was achieved by expending additional labour and support energy in the ratio 4 x lo9 J/man hour. Separate calculations showed that maintenance of hygiene and disposal of effluent accounted for over half the total energy cost of factory operations. 1. Introduction Several analyses have been made to ascertain the total consumption of energy involved in the production, processing and distribution of food. Steinhart and Steinhartl showed that in the USA in 1970, the overall inputs were 2.2 x l0l8 J in the farm sector, 3.5 x 1018 J in catering industries and the home. Industrial use of energy in food processing is clearly a large proportion of the total. In the United Kingdom Leach2 has estimated that the inputs of energy for food production, pro- cessing, delivery and final preparation in the home are about 34 x l o 9 J per person per year and that food processing and wholesale and retail distribution accounts for over a third of the total. Such studies and those of others (notably Hirst3 in the USA and Gifford and Millington4 in Australia) deal with the whole system of food provision, including the growing of crops and animals. Few studies have been made of individual items of food, although Leach2 has analysed in detail the support energy required to the point of retail sale to produce a loaf of bread and, using the UK Input-Output Tables,5 has estimated the support energy required by major sectors of the food and drink industries of the UK. The present study was undertaken to assess, in as direct a way as possible, the support energy required to produce meat and meat-containing foods. The investigation included detailed estimation of support energy required to transport live animals from farm to abattoir, to slaughter, process them, and to package, warehouse and deliver the final products to the retailer. 2. Methods The investigation was carried out in the NE and E of Scotland, where almost 50 of Scottish meat production is located. Cattle and pig meat production were studied in the premises of three major meat processing firms and in five private butchers shops. The latter were selected at random in the Falkirk-Stirling area and two of them, besides selling manufactured meat products which they purchased wholesale, also prepared small quantities of sausages and pies. All butchers prepared 0022-5142/78/0200-0172 $02.00 0 1978 Society of Chemical Industry 172 Support energy in meat processing industry 173 considerable amounts of mince. All firms involved in the study provided information freely and it was on the basis of analysis of their records, supplemented by additional measurements where necessary, that estimates of energy consumption were made. Many difficulties arose, however, with respect to precise allocation of energy costs to particular products because of the complexity of the overall operations. Thus, certain initial costs, such as those of transport, lairage and slaughtering, had to be distributed over a number of final food products-fresh meat, edible fats, sausages, pies and other products. Distribution of energy costs equally applied to effluent disposal and provision of staff amenity. In addition, a trade in parts of carcasses which related to seasonal demands for particular manufactured products created additional distribution and summation problems. The conventions adopted to deal with these difficulties are given below. The allocations of initial energy costs to final products were made in proportion to the mass of the animal component in the final product. The energy required to render technical fats, to manu- facture bone meal and to deal with blood was counted as a slaughter cost and was not separately assigned to these by-products. Since skins were often sold fresh, no energy was allowed for any subsequent transport or tanning of them. In these various ways the major part of the by-product costs was allocated to the final food product. In our opinion this approach is sensible because the primary process involved is the production of food and it is necessarily associated with the secon- dary processes of by-product disposal. Effluent costs were allocated in proportion to water use in the various parts of the overall processing, while the energy costs of provision of hygienic facilities (where they could not be allocated to a part of the process), laundry, cleaning, canteen and admin- istrative costs, were allocated in proportion to the manpower employed in each defined sector. For the energy cost of hygiene, however, dirty tasks such as slaughtering, butchering and bone meal manufacture were charged at a rate per caput which was three times that charged for the cleaner operations which, from observation, required smaller quantities of hot water and steam. Where a firm purchased a carcass or side from elsewhere to augment the production of a particular product, the assumption was made that the support energy expended up to the point of purchase was the same as that which would have been incurred had the meat been processed within the plant. These conventions are peculiar to the meat industry and obviously have some effect on the final estimates, but are not thought to be of major dimension. Other conventions were adopted in the estimation of energy costs of particular items and are listed below. 2.1. Direct consumption of fuel and power Input energies per unit of fuel derived from the studies of Leach and Slesser6 and were taken to be 14.7 x 106 J/kW h for electricity, 138 x lo6 J/Therm for gas and 187.3 x 106 J/gal for both heavy and light fuel oil. In many instances individual electrically powered machines in a department of a factory were not separately metered. To estimate power consumption the fraction of total plant operating time during which the machine was switched in was multiplied by the power rating of the machine. No allowance was made for any effects on consumption of start up or shut down. Direct tests using power meters of this method of assessment showed it to be accurate to & 5 %. 2.2. Energy cost of replacement of capital equipment Following the practice adopted by Blaxter? a value of 136 x lo6 J /Ll capital depreciated at 1974 values was used to cover the cost of replacement of plant and machinery. 2.3. Energy cost of packaging materials purchased Most of the purchased inputs of packaging consisted of low density polythene and polypropylene for vacuum packing and shrink wrapping of meat, trays of foamed polystyrene far sausage packing and aluminium trays for pies. Nylon reinforced sachets were used for large catering packs and joints. In addition, composite aluminium-polythene laminates were used in decorative packs, while card- board boxes were employed in bulk packaging. The weights of materials per final package were determined and the energy costs per ton of packaging material were those listed by Berry and Makino.8 These are known to be applicable in the United Kingdom. 174 J. I(. Jacques and I(. L. Blaxter 2.4. Energy cost of transport The information made available by the firms allowed energy costs of transport to be estimated directly from vehicle life, fuel consumption and cost of tyres. Component factors have been listed9 in terms of cost. 2.5. Energy cost of non-meat additions to products Sausage and pie formulations are proprietary secrets. A pork pie contains flour and rusk ingredients, while a Cornish pasty also contains carrclts and other root vegetables. The support energy cost of production of these items has been given a representative value in Table 2 in the column referring to final product, but this support energy has been omitted from the column referring to the energy per unit of deboned meat in pies and other products in which meat is but one ingredient. Total support energy for baked bread and pastry products (including energy to grow the wheat grain) has been taken at 1 1 x lo9 J per ton; ex farm gate figures for (raw) vegetables lie generally between 1 and 3 x loy J per ton (UK) (M. Green, personal communication) and the slightly pessi- mistic figure of 3 x lo9 J per ton has been used in this work. In the case of calculations based on deboned meat, the energy associated with cooking pies and pasties is attributed to the meat on a simple proportional basis. 2.6. Energy cost of labour The energy required to support the personal and domestic life of factory or shop workers is not considered. Energy expended in canteen facilities in larger factories is, however, included as well E S those facilities concerned with hygiene within the factory. The convention to ignore the energy required by labour for personal support is that used by Blaxter7 but not by Leach2 in energy accounting studies. 2.7. Calculation and expression of results The whole complex process of manufacture of products was separated into stages which coincided with divisions of the factory or shop, and energy costs incurred at earlier stages were allocated in proportion to quantities of meat entering the next stage. Results are finally expressed per ton of saleable product. In addition, results are calculated per ton of meat; this requires careful definition of the term meat and we distinguish between meat defined as dressed carcass weight and deboned meat with surplus fat removed and with edible offal added back as appropriate. Table 1 gives the factors which have been used in this work to convert live animal units to carcass or deboned meat. For pies, sausages and bacon/ham products, the calculation initially evaluated the support energy per ton of product first; for these products the energy inputs per animal were calculated back using the factors in Table 1 . The converse applied to basic butchery operations. In deriving Table 1, the following conventions were employed: for cattle, the dressed carcass was taken to be 55% of live weight. The meat yield from the carcass, combined with edible offals, referred to in Table 3 as deboned meat was taken to be 41 % of the live weight. Edible fat from the carcass and offals was assessed as 5.2% and industrial fats as 4.1 of live weight. Total bone Table 1. Number of animals required to produce 1 ton of carcass or deboned meat Factors to convert to: 1 tonof Live 1 ton of deboned animal carcasses meat Pigs 1 .o 1 8 . 6 22.2 Cattle 1 .o 3 .5 4 . 7 Support energy in meat processing industry 175 and hoof was estimated to be 13 %, 7.7 % deriving from the dressed carcass and 5.3 % from the non-carcass component. For pigs, the dressed carcass with head included was taken to be 73 % of live weight. Edible offal was assumed to account for 5 % and bone for 14% of the dressed carcass. The edible meat content, including edible offal, thus represents 56% of the live weight (excluding the head). This somewhat arbitrary choice of values, based on anatomical and butchery evidence, formed the basis for all derived calculations. The data are presented firstly in operational terms, summarising the energy costs involved in each stage of the process. They are then recombined on a flow basis to give the energy costs of the final products. Transport of animals to the abattoir is dealt with first, then the processing costs, and lastly the transport of meat and meat products and the support energy costs incurred at the retail outlet. 3. Results 3.1. Transport of animals to abattoirs The energy cost of transport of an animal to the point of slaughter is the product of energy cost per vehicle mile and length of the journey (including any unladen running) divided by the number or mass of animals transported per journey. Running and depreciation costs for the fairly standard 3-axle 12-16 ton gross laden weight vehicle, consuming fuel oil at the rate of 12 mpg and with a capital value of E l 0 000 and an amortisation life of 5 years, were computed from factory records. Analysis of day-by-day delivery notes provided estimates of distances travelled and number of animals transported. The results are given in Table 2. Table 2. Energy cost of transporting live animals to the point of slaughter: large abattoirs Energy (J x lo6) consumed per mile Average one-way distance transported Per ton Average energy per animal delivered Animal (miles) Per animal live weight to factory from farm (J x lo9) Cattle Pigs 40 1.38 2 .6 25 0.30 3.3 0.110 0.024 They show that energy costs/ton-mile were 2.6-3.3 x lo6 J (1.62.1 x lo6 Jitonne-km). These are lower than the figure of 4.0 x lo6 J/ton mile calculated by Leach* from data of the UK Transport and Road Research Laboratoryg with an arbitrary correction of 25 % for depreciation, tyres and repairs (one-way distance) as used by Blaxter.? The lower value largely reflects the considerable efficiency of transport organisation in terms of avoidance of part loads exerted by the firms studied. Expressed per ton of deboned meat entering the factory (see Table 7), the energy cost per ton of animal transported expressed as deboned meat was the same for pigs and cattle at 0.5 x lo9 J/ton. 3.2. Meat factory operations In factories which produce a number of different products, operations follow a logical sequence and this dictates departmentalisation of the enterprise. The initial analysis was based on these departments and Table 3 summarises the operations involved and the energy costs incurred in each. From this primary information the energy inputs into the final products were computed with the results given in Table 4. In this table all by-product energy costs are assigned to the final products. The magnitude of the support energy required may be placed in perspective by considering that the heat of combustion of muscle tissue devoid of fat is approximately 5.4 x log J/tonne. The support energy required to manufacture and package sliced bacon is thus about eight times the heat of Table 3. Energy inputs into operations in meat factories processing cattle and pigs Energy input to the sector (J x lo9) Final (F) or Per ton Per ton of Labour input Intermediary (I) or dressed carcass deboned meat man hours By-product (B) i.e. not including (including per ton Operational sector Processes included Product emerging Per animal offals edible offal) deboned meat 1. Pig slaughter and Lairage; slaughter; removal of Carcass sides (I) 0.45 8.37 9.99 1.58 chill blood, hair, head, backbone, Bones and inedible gut and offal; cleaning of carcass and chilling for 18 h at 3'C Edible fat (I) offal (I) Edible offal (I) Inedible fat (I) (Blood B) 2. Cattle slaughter Lairage; slaughter; removal of Carcass sides (I) and chill blood, skin, edible and Bones (I) inedible offal; cleaning and chilling of carcass for 30 h at 3OC Edible fat (I)Edible offal (I) Inedible offal (I)Inedible fat (I) Blood (I) Skin (B) 3. Beef boning and Removal of major bones and Fresh joints (F) jointing division of carcass into parts Joints for cooked Sausage meat (I) Pie meat (I) Bones (I) Fat (I) for subsequent processing meat preparation (1) 2.36 8.26 11.09 2.230.68 2.38 3.20 3.104. c t4 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Bone meal plant Casing preparation Lard and suet production Bacon butchery Bacon curing Bacon dressing and vacuum packing Fresh pork processing Ham production Sausage production Sausage filling Meat pie preparation Cooked meats Special prepared meats Receives all bones and inedible offal from pigs, produces bone meal (also a proportion of blood) manufactures sausage casings Receives gut from pigs and Receives and processes edible fats from pigs and cattle Dissection of sides, removal of bones Smoking and brine curingTrimming, slicing and packaging Curing and rolling of joints for Smoking and boiling of joints for Butchery to produce sausage meat Filling of sausages and packaging Mixing and preparation of casing, cooking and packaging of pork and beef pies Preparation and cooking of large roasts for sale as cooked meat Specialised production of meat dishes, and a variety of cooked meat products of baconhamham and bacon and pork pie meat Bone meal (B) Inedible offal (1) Inedible fat (I) Sausage casings (I) Lard (F) Suet (F) Inedible (I) Bone (I) Fresh meat (I) Joints for curing (I) Cured sides (I) Cured hams (I) Packed bacon (F) Joints for ham and Ham (F) Bacon (F) Sausage meat (I) Pie meat (I) Sausages (F) Pork pies (F) Meat pies (F) Cooked meat (F) Prepared meats (F) bacon (I) Pigs 0.43Cattle 1.00 0.13 Pigs 0.07 Cattle 0.10 0.23 0.40.720.207 2.290.22 (Pork) 1 .48 (Pork) 2.06 (Pork) 15.3 (Beef)70.0 (Beef) 14.8 (Pork) 4.61 (Beef) 0.97 (Pork) 8.0 3.5 2.421.3 0.359.554.7 2.891.55 0.47 5.28.915.9 4.651.0 4.87 33.0 45.7 72.0329.0 7.1 0.06 0. I 8.32.0 5.3 9.01 .o 11.6 22.0 23.710.0190.0 The bold figures represent the primary calculations; values in the other columns were derived using the factors in Table 1. 118 J. K. Jacques and K. L. Blaxter Table 4. The energy input and labour costs incurred in operations in meat factories leading to the production of items of fooda Energy cost (J x I09/ton) Labour input Food product Deboned meat Producta as sold man hours/ton product as sold Side of pork Jointed pork (wrapped) Hams (wrapped) Cured boiled joints (wrapped) Smoked and cooked joints Bacon (cured, sliced and packed) Pork sausages (65 % meat) Pork pies (46 % meat) Side of beef Jointed beef (wrapped) Beef pies (34 % meat) Factory roasted beef (wrapped) - 26.6 30.7 81.7 98.2 47.7 58.6 77.2 19.46 86.3 348.5 - 17.7 26 .6 28 .5 99.5 124.0 44 .0 40.9 42.54 16.26 19.46 38 .6 554.3 1 .8 2 5 10.1 19.8 20.8 9 . 3 22.7 34.8 2 .1 5 . 1 32.0 196.0 ~ a Some of the apparent discrepancies in the table between final product cost and deboned meat content arise from uptake of water during bacon curing (about 8 %) and losses of water by evaporation on cooking certain of the products. combustion of the muscle tissue it contains. This energy subsidy does not include support energy required to produce the pig destined for bacon production ; these aspects are considered later. Tables 3 and 4 do not separate costs of specific and essential aspects of the production process such as the maintenance of high hygienic standards or the disposal of effluent. These two are linked and separation of them from the remainder suggests that together they account for about 55% of the total energy cost of the more sophisticated products. 3.3. Distribution of meat and meat products to the point of sale Deliveries of meat and meat products from factories to wholesalers or retailers incur energy costs dependent on the type of product and the mode of transport. The firms concerned operated guarantee systems for delivery and most vehicles were not operated at full load capacity. The vehicles used were all insulated and refrigerated. The energy cost of operation of the refrigeration was included. Transport costs were broken down into categories according to type of vehicle and geographical groupings with the results shown in Table 5. The figures apply to journeys with actual loading. Table 5. Energy cost incurred in transport of meat and meat products by refrigerated transport Energy consumed Type of distribution Type of vehicle (J x 1O6j/ton mile Mean total costiton (J x 109) Wholesale distribution of meat to Scottish distributors Wholesale distribution of meat to major English distributors Delivery vans distributing to the Highland Region Delivery vans from east and central Scottish warehouses to retail premises 20 ton 4 axle 20 ton 4 axle 12 ton 2 axle 2 ton 2 axle articulated truck 4 . 0 f 0 . 0 2 articulatea truck 2.47 t 0 . 0 2 delivery vehicle I l , O 8 ? 0.04 sales van 13.78+0.003 1.74 2.31 2.58 1.98 Support energy in meat processing industry 179 3.4. The small butcher and retail outlet The small butchers not only sold meat they prepared from animals killed in local slaughterhouses, but also marketed prepared meat products which they purchased from wholesalers who had obtained them from large central meat factories. From the five shops studied, an estimate was made of the energy costs incurred in the small-scale processing of meat. To do this, however, it was necessary to assume that the energy costs of all those processes up to the stage of a chilled carcass in the local abattoir were the same as those measured in the meat factories. This again implies a charging of the energy requirement for disposal of by-products against the edible food produced. In addition, since sheep slaughtering was not included in the studies at meat factories, it was as- sumed that the costs to the end of the chill stage per ton of meat were the same for sheep as for cattle. Table 6 summarises the calculations. Table 6. Energy cost of the processing of meat by high street butchers in Central and East Scotland. (The median s t a r was 10 persons, the edible meat sold was 208 tonnes, and the slaughterings were in the ratio 5 cattle beasts: 3 sheep: 1 pig) Total (J x I 09) Per ton of edible meat (J x lO9)/tonne Transport of live animals to local Cattle abattoirs via auction marts Sheep (Average 65 miles) Pigs of by-product disposal Cattle to shops Sheep (Average 40 miles) Pigs Direct fuel consumption in the shop for refrigeration display, lighting, mincing etc. Replacement of machinery, plant and building Cost of slaughter and associated costs Cost of transport of meat from abattoirs 5; } 69 0.33 7 3394 16.3 l; } 18 0.09 482 2.31 136 0.65 1 Total 4099 19.7 4. Discussion There is considerable complexity in the meat processing industry. This is seen at the level of overall organisation of firms which range from the small butcher who purchases animals in an auction market, contracts for their slaughter at an abattoir and then processes the carcasses in his shop, to the large meat factories which purchase mainly on contract, produce a variety of products, some of which are highly sophisticated, for sale to wholesalers or to supermarkets. The complexity is also evident at the operational level; the overall process of producing meat and more particularly meat products entails a complex integration within a factory of a series of tasks, and, in addition, the provision of facilities for disposal of a number of separate by-products. The precision of the final estimates of the quantities of support energy required to produce meat and meat products, depends largely on an ability to separate and to assign the components of energy subsidy. It is thought that the final estimates are probably accurate to within & lo%, although there is probably a greater uncertainty about lard production, roasted joints and some prepared meats. The data presented on the energy and labour costs of producing meat and meat products show, as expected, that the imparting of convenience. to foods is associated with a considerable increase in energy subsidy and labour usage. Cooking, and especially roasting of joints, in the factory is particularly energy expensive; this factory processing, however, results in a saving of energy and labour in the home. Generally, apart from cooked meats, the energy cost of prepared products expressed per ton of meat is about twice that of primary joints. As far as labour is concerned, for products other than pies and sausages, the expenditure of additional labour is proportional to the 180 J. K. Jacques and K. L. Blaxter expenditure of additional energy; convenience is achieved by expending energy and labour in the ratio 4 x 109 J per man hour. In the production of a sausage or a pie, however, the ratio is 1 x 109 J per man hour or less; the more sophisticated the uncooked product the greater the use of manpower. There is, however, no proportionality between final prices of products and the energy input or the manpower cost incurred in their production. Thus at the time the investigations were made the market prices of pork joints and pork sausages were approximately the same while the prices of cooked beef pies were less than those of beef joints. This may well reflect the integrated nature of the whole meat processing operation, but certainly appears anomalous. A comparison can be made between centralised factory production where slaughter and process- ing is combined and high street operations where slaughter and small-scale butchery are separated and are on a much smaller scale. Here there are limitations to the data. No energy costs for sewage disposal have been assigned to local butchers shops nor to other services of similar nature provided by local authorities. Superficially it would appear that the overall cost of collection of cattle and delivery of meat in joints to the point of sale is greater for the factory process than for the small- scale operation, the relevant figures being about 27 x lo9 J/ton for the factory process and about 20 x 109 J/ton for the small scale one. Apart from failure to include certain energy costs, differences between the enterprises in terms of the final products make firm conclusions difficult. Quantitative aspects of the total energy consumption in meat and meat production for an animal moving through the whole production sequence-farm, factory and distributive outlet-can be calculated. These integrated processing energy costs per animal can only be approximate for they depend on assigning proportions of final product to an animal. Mean values for these proportions were calculated from a sample of 50 000 pigs and 2000 cattle. Roughly 41 % of the edible (carcass plus offals) of pigs was marketed as sliced bacon (20%) or sides of bacon (21 %); 25% of the edible carcass was marketed as cooked ham or pork joints (16.5%) and uncooked pork joints (8.5%). Meat in various sausage formulations accounted for 27 %, and 7 % was accounted for in pork pies. Table 7. The overall support energy cost of production, transport, slaughter, processing and distribution of meat from cattle and pigsa (All units are J x lo9) Pigs Cattle Per ton Per ton Per Per ton deboned Per Per ton deboned beast carcass meat beast carcass meat Pre-factory inputsb Transport (excluding transport) Live animal bProduct distribution Factory butchering and processing Totals Available food energy Support energy input Food energy output 2.5 41.4 44.2 15 52.6 70.6 0.02 0.45 0.53 0.11 0.39 0.52 0.08 1 . 5 1.88 0.40 1.40 1.88 2.71 50.4 60.1 8.7 30.4 40.9 5.3 93.8 106.7 24.2 84.8 113.9 16.3 12.0 14.4 (Pork) 7.4-6.5 9.4 (Ham) a The proportions of various meat products derived from the animals i s given in the text. * Costs incurred on the farm were based on total inputs of 25 x lo8 J/ha for barley grain and 12 x lo9 J/ha for Cattle were taken to require 1.25 ha equivalent of appropriate cereals and pigs 0.088 ha equivalent of appropriate intensive pasture rearing. cereals. Support energy in meat processing industry 181 For beef, the picture was relatively simple, with roughly 7% of edible carcass meat and offals being used in meat pie manufacture, 10% as sausage meats, a small percentage (0.5%) as pre- roasted joints, and the rest as large joints of fresh meat (often vacuum packed). Table 7 summarises the calculations of inputs of support energy at the farm based on estimated grazing and cereal requirements and the transport and animal processing costs. The table shows that animal transport is a small item because both animal and product transport are specialised and generally well planned operations. Butchery and factory processing costs are surprisingly small for cattle compared with the support energy required at the farm level, but none the less make a con- siderable contribution to the total. With pigs the processing and butchering support energy costs exceed those incurred on farms in their production. It appears from the calculation that the support energy used in pig meat production is higher than that for beef production per Joule of final food product. The final figures in Table 7 giving the support energy required to provide unit energy in food may be put into perspective by comparing them witfi values for processed cereals and root vegetables. These range from 3 to 5 J/J human food. References 1. 2. 3. 4. 5. 6. I 8. 9. Steinhart, J. S . ; Steinhart, C. E. Science, N . Y., 1974, 184, 307. Leach, G. Energy and Food Production, London and Washington, International Inst. for Environment and Development, 1975. Hint, E. Science, N. Y., 1974, 184, 134. Gifford, R. M.; Millington, R. J. Energetics of Agriculture and Food Production with special emphasis on the Australian situation, Adelaide, UNESCO symposium on Energy and how we live, 1973. Central Statistical Office. Input-Output tables for the UK 1968, London, HMSO, 1973. Leach, G. ; Slesser, M. Energy Equivalents of Network Inputs to Food Producing Systems Strathclyde University, Glasgow, 1973 Blaxter, K . L. J. Sci. Fd Agric. 1975, 26, 1055. Berry, R. S.; Makino, H. Tech. Rev. 1974, 76, no. 4. Everall, P. F. The effects of road traffic conditions on fuel consumption, Transport and Road Research Lab. Report No. LR226, 1968. 12*


View more >